1. Field of the Invention
This invention generally relates to the field of optical devices, and more particularly to a controllable demultiplexer/multiplexer.
2. Description of the Related Art
Optical devices having phased arrays of waveguides, also referred to as Arrayed Waveguide Grating (AWG) devices, are often used for optical multiplexing and demultiplexing applications in optical networks. AWGs, in particular, are suitable for handling inputs having a large number of wavelengths (or channels). AWGs are conventionally planar devices having a plurality of substantially parallel waveguides, each differing in length from its nearest neighbors, coupling two opposing star couplers. Most conventional AWGs are passive devices, such as shown in U.S. Pat. No. 5,002,350.
For example, a schematic of a conventional AWG is shown in FIG. 1. The corresponding spectral output response of the conventional AWG is shown in FIG. 2. In this conventional planar design, the conventional AWG 1 includes an input slab 30, a waveguide array 45, and an output slab 50. Input slab 30 can operate as a 1xc3x97N splitter. In FIG. 1, the input signal 10 enters at the entrance plane of the slab 30 through one of the input port(s) 20-1, . . . , 20-s. The optical signal spreads throughout the xe2x80x9cfree-spacexe2x80x9d slab 30, and is distributed among M number of ports at side 31 of the slab 30.
Waveguide array 45 includes M number of substantially parallel planar waveguides 45-1, . . . , 45-m, having path lengths l1, . . . , lm. Adjacent waveguides have an incremental path length difference of xcex94l=lxxe2x88x92lxxe2x88x921. The waveguides 45-1, . . . , 45-m end with ports 40-1, . . . , 40-m on side 51 of output slab 50. The output ports 40-1, . . . , 40-m are considered in the art to form a diffraction grating. Output slab 50 provides Mxc3x97N coupler operation in which the M signals coming from M parallel waveguides 45-1, . . . , 45-m are combined and allowed to interfere, such that each wavelength is directed to converge on a different output port 65-1 to 65-n of the device at side 57 of the slab 50. All these parts can be formed on a silicon substrate by conventional means. See e.g., C. Dragone, IEEE Photonics Technology Letters, vol. 3, no. 9, pp. 812-815 (September 1991). Once the AWG is fabricated, all the path lengths of the different arms are fixed, which makes the device""s wavelength spacing permanent because channel spacing is generally determined by the incremental path difference xcex94l of the waveguide array 45 of the AWG.
As mentioned above, conventional AWGs utilize substantially parallel waveguides that are permanently fixed in their respective physical path lengths. The impact of this fixed physical path length difference xcex94l on current DWDM network system when these AWGs are deployed is the pre-determination of the overall channel spacing xcex94xcex of the whole network. This decision affects all network components and equipment deployed in the network such as: OADM, WADM, OXC, laser wavelength channels, etc. Once this optical network is deployed, any future upgrade (in terms of increasing the number of wavelength channels by reducing the channel spacing) would require replacing all these previously deployed AWGs with new AWGs having narrower channel spacing. Another approach is to complement all the deployed AWGs with optical interleaved filter (OIF) pairs by engineering them in the network. These upgrade scenarios are necessary when the optical amplifier""s useful spectral range reaches its limit.
In both of these approaches, the development and implementation of hardware upgrades are expensive, time consuming and could result in a more complicated overall network. Furthermore during the upgrade, part of the network operation must be taken off-line or shut down in order for the deployed AWGs to be replaced.
According to one embodiment of the present invention, an optical device comprises a beam distribution element to receive an input optical signal comprising one or more wavelengths and to distribute the optical signal into a plurality of beams. The optical device also comprises a variable path length element to receive the distributed optical signal from the beam distribution element, where the variable path length element comprises a plurality of path sections, where a length of at least one of the path sections is variable. The optical device further comprises a beam interaction element to receive the plurality of beams from the variable path length element, wherein the plurality of beams interact such that each wavelength can propagate to a different output. The optical device can further include a plurality of exit ports to receive the demultiplexed beams, where a first exit port receives a first demultiplexed optical signal having a first wavelength and a second exit port receives a second demultiplexed optical signal having a second wavelength different from the first wavelength. A controller operatively coupled to the variable path length element can be provided to vary the length of one or more of the path sections. The variable path length element can include an optical switch fabric, such as a two dimensional switch fabric or a three dimensional switch fabric.
In a preferred aspect of this embodiment, the variable path length element can be constructed from an optical switch fabric based on an array of MEMS mirrors, a liquid crystal based switching array, or a bubble type switching array. In an alternative aspect of this embodiment, the variable path length element can be based on a three dimensional switch fabric constructed from opposing moveable mirror arrays.
In another preferred aspect of this embodiment, the variable path length element comprises a MEMS mirror switch array, where at least one of the mirrors is tiltable or partially actuatable to provide variable optical attenuation of the reflected optical signal. In other preferred aspects of this embodiment, the variable path length element can include a liquid crystal based switching array, a bubble type switching array, or a combination of MEMS, liquid crystal and/or bubble type switching arrays, in which at least one of the switching elements is partially actuatable to provide variable optical attenuation of the reflected optical signal.
According to another embodiment of the present invention, a method of demultiplexing a multiplexed optical signal includes distributing the optical signal into a plurality of beams; directing the plurality of beams to a variable path length element, wherein the variable path length element comprises a plurality of path sections corresponding to a number of distributed beams, wherein a first beam of the plurality of beams propagates along a first path section and a second beam of the plurality of beams propagates along a second path section, wherein the first path section is set to a first path length in a first state and the first path section is set to a second path length in a second state, wherein the first and second path lengths are different, wherein the second path section is set to a third path length in a first state and the second path section is set to a fourth path length in a second state, wherein the third and fourth path lengths are different; and directing the first and second beams from the variable path length element into a beam interaction element, wherein a first exit port receives a first output beam having a first wavelength and a second exit port receives a second output beam having a second wavelength, said first and second wavelengths being different.
The devices and methods of the present invention results in a number of advantages over prior art devices and methods. The channel spacing of the demultiplexer devices of the current invention may be changed by the user, allowing greater flexibility in network design and implementation.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework to understanding the nature and character of the invention as it is claimed.
Other advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.